The present invention relates to generally an improvement in a permanent magnet alloy of an inter-metallic compound consisting of one or more rare earth elements and Co and more particularly to an improvement of a permanent magnet alloy of a Cu-added R.sub.2 Co.sub.17 type with a lower content of a rare earth element.
As is disclosed in for example Japanese unexamined Patent Publication No. 1397/75, it has been well known in the art that an alloy consisting of Co, Fe, Cu and rare earth metal or metals in combination mainly consisting of Sm and Ce the composition of which is expressed by a formula EQU R(Co.sub.1-x-y Fe.sub.x Cu.sub.y).sub.A
where R=a rare earth metal or a combination of rare earth metals mainly consisting of Sm and Ce, EQU 0.01.ltoreq.x.ltoreq.0.03 EQU 0.05.ltoreq.y.ltoreq.0.25, and EQU 6.5.ltoreq.A.ltoreq.8.0,
exhibits excellent remanance (Br) and coercive forces (.sub.B H.sub.c, .sub.I H.sub.c). Furthermore it has an energy product ((BH)max) as high as 25 M GOe. Therefore, it has been used in various fields. However in this magnet series, a large amount of Cu substitution is required for attaining desired degree of precipitation hardening. As a result, Br is decreased and a maximum remanance Br is of the order of 10,500 G. Furthermore, the decrease in Curie point due to Cu substitution results in a decrease in thermal stability. Fe substitution contributes to an increase of remanance Br, but an excessive Fe substitution results in a decrease in coercive force. As a consequence a maximum Fe substitution x is in the order of 0.1. Moreover, the value of A required in order to increase coercive force and to obtain a better squareness of a hysteresis curve is in the order of 7.0-7.5, therefore a high remanance Br cannot be obtained.